In QuickBooks Online, it depends on how far your bank can let the QuickBooks download or get their transactions. If you are referring to bank transactions, we can import the transaction if it wasn't downloaded automatically.
Here's how if your account is connected to online banking:
Go to Transactions, then Banktransactions
Select the blue tile for the account you want to upload the transactions into.
Select the Link account▼ dropdown and then Upload from file.
Select Drag and drop or select files and select the file you downloaded from your bank. Then select Continue.
In the QuickBooksaccount▼ dropdown, select the account you want to upload the transactions into. Then select Continue.
Follow the onscreen steps to match the columns on the file with the correct fields in QuickBooks. Then select Continue.
Select the transactions you would like to import. Then select Continue.